Electrical switching devices are well known in the field of medium and high voltage switching applications. They are e.g. used for interrupting a current when an electrical fault occurs. As an example for an electrical switching device, circuit breakers have the task of opening contacts and keeping them far apart from one another in order to avoid a current flow, even in case of high electrical potential originating from the electrical fault itself. For the purposes of this disclosure the term medium voltage refers to voltages from 1 kV to 72.5 kV and the term high voltage refers to voltages higher than 72.5 kV. The electrical switching devices, like said circuit breakers, may have to be able to carry high nominal currents of 5000 A to 8300 A and to switch very high short circuit currents of 83 kA to 80 kA at very high voltages of 550 kV to 1200 kV.
Because of the high nominal current, the electrical switching devices of today require many so-called nominal contact fingers for the nominal current. When disconnecting (opening) a nominal or short circuit current within the electrical switching devices, the current commutates from nominal contacts of the electrical switching device to its arcing contacts. When connecting (dosing) the nominal contacts of the electric switching device, also the arcing contacts are connected. They normally comprise as a first arcing contact arcing contact fingers arranged around the longitudinal axis of the electrical switching device in a so-called arcing finger cage and, as a second arcing contact, a rod which is driven into the finger cage.
During the closing and opening process of the electrical switching device an electric arc forms between the first and the second arcing contact, which damages the contacts over time. In order to minimize this damage the electrical switching devices contain a fluid used to quench the electric arc as fast as possible. Another measure is to limit the time period for the entire closing and opening process of the nominal and arcing contacts, particularly the time period or time interval between contacting the nominal contacts and contacting the arcing contacts or between separating the nominal contacts and separating the arcing contacts. This time constraint results in the necessity of accelerating and decelerating the nominal contact and the arcing contact on one side of the electrical switching device according to the given time period. The contacts have to have a certain cross-section in order to be able to carry the required current. Very high voltage circuit breakers require a longer distance between contacts in an opened state in order to avoid electrical breakdown. Hence, considerable forces are necessary to accelerate and/or decelerate the contacts and the additional moving parts of the switching device. These forces may lead to increased mechanical stress on the moving parts of the contact arrangement and even to mechanical failures, thus reducing the lifetime of such an electrical switching device. Furthermore, particles are generated during the switching process of the circuit breaker, which can result in dielectric failures.
The invention starts from EP 0 696 040 A1 which discloses a circuit breaker with an auxiliary gear for double-motion. An independent movement of arcing contact pin and nominal contact on one side of the circuit breaker is provided by a cog wheel linked to two force-transmitting levers. The cog wheel is for introducing the force from an axially movable shaft.
DE 10 2012 205 224 A1 discloses a circuit breaker with an auxiliary gear for double-motion. An independent movement of arcing contact pin and nominal contact on one side of the circuit breaker is provided by a two-armed rigid lever with integrated cam disk for driving the arcing contact pin.
DE 196 22 460 A1 discloses a circuit breaker with an auxiliary gear for double-motion. An independent movement of arcing contact pin and nominal contact on one side of the circuit breaker is provided by a two-armed rigid lever linked to two force-transmitting levers. The two-armed rigid lever has an integrated long hole for introducing the force from an axially movable shaft.
WO 2012/155952 A1 discloses a circuit breaker with a first gear on a drive side for coupling the driven nominal contact via levers nonlinearly to the arcing contact tulip and with a second auxiliary gear distant from the drive side for reverse movement of the arcing contact pin.
FR 2 491 675 discloses a circuit breaker with an auxiliary gear for providing double motion of both pin and tulip. A semi-mobile pin is disclosed which is spring-loaded and can be retracted abruptly by the force of the spring.
EP 1 930 930 A1 discloses a circuit breaker with a non-linear auxiliary gear for double-motion.